Magnesium base allot



' the desired properties prior to use.

Patented Sept. 25, 1945 MAGNESIUM' BASE ALLOY Robert s. Busk, Midland, Mich-, assign-or to The Dow Chemical Company, Midland, Mich., a corporation of Michigan.

No Drawing. Application April 13, 1942, Serial No, 438,784

Claims. (cl. 75-168) The invention relates to magnesium and in particular concerns alloys of this nature having reduced burning or oxidation characteristics in the molten state.

Magnesium alloys are now widely used in the industrial and structural arts for forgings, castings,'and extruded shapes where a light weight metal having good strength properties is highly desirable. It is, of course, generally necessary to melt the magnesium as produced commercially and alloy it with other elements to give it Additionally, it may be necessary to remelt the so-formed alloy a number of times as when it is used for casting operations. It is well known that when magnesium and its alloys are handled in the molten state it is necessary to maintain the metal under a. protective blanket of a suitable flux in order to control the oxidation and burning of the metal to the extent that it may be commerbase alloys 1 cially used and, even then, an appreciable waste occurs due to burning. -In case the material is to be used in casting operations more waste occurs as the molten metal is ladled from the melting pot and poured into molds since. this operation is carried out while the metal is in direct contact with! air. It is, therefore, the principal object of the invention to provide commercial alloys of magnesium exhibiting markedly decreased burning tendencies upon exposure to air.

Another object of the invention is to provide a magnesium base alloy which may be ladled in the molten state andpoured into ingots without exhibiting marked burning tendencies! Other objects and advantages of the invention will be apparent as the description proceeds.

My invention is based on the discovery that the burning characteristics of magnesium metal as well as some of the well known commercial magnesium alloys are greatly improved by alloying therewith a comparatively small amount of potassium. The quantity of potassium to be added to produce the desired effect ranges between about 0.001 to 0.05 per cent. "Specifically it has been found that the above noted effect is obtained by adding potassium to agnesium metal or magnesium alloys in which a uminum, manganese, silver, and zinc are present either alone or in combination in the usual amounts for commercial alloys of magnesium containing these elements. Such alloys may contain from 1 to. 12 per cent ofaluminum, 0.01 to 3 per cent of manganese, depending upon the amount of aluminum present, 1 to 10 per cent ofsilver, and from 1 to 10 per centoi zinc, providing the magnesium content is maintained above about '80 per cent. .In the case of manganese if the amount of alu-. minum exceeds about 2 per cent, more than about 0.5 per cent of manganese .cannot be alloyed with a magnesium-aluminum alloy. It will be understood that the above alloys may also contain the ordinary impurities that are found in the commercially known alloys, such as traces of iron,

sium. v Table Per cent composition magnesium-remainder Crucible burn Al Zn Mn Marked burning. Im roved over xample 1.

9 2 0. 2 Marked burning. 9 2 0 2 Greatly improved over Example 1.

The tests labeled "Crucible burning were made using alloys compounded by adding the alloying ingredients with stirring to a. quantity of molten magnesium maintainedunder a suitable fluxblanket. The test consisted in skimming the flux blanket from the surface of theme": and observing the comparative burning in the presence and absence of potassium. In the case of the tests labeled Ingot burning the molten metal, compounded in the foregoing manner, was poured into a suitable ingot mold and the'surface of the metal examined from time to time to determine the degree of oxidation in the presence and absence of potassium.

It is clear from an examination of the table that the new alloy provides a distinct improvement as regards burning and oxidation over a well known commercial magnesium alloy. This improvement is observed in both the open crucible and when the metal is poured in ingot molds.

Although the addition of the stated amounts of potassium greatly decreases the burning tendency of magnesium or the noted alloys, it has been discovered that if the potassium content of Ingot burning v 2 e the alloy exceedsthe upper limit 010.05 per cent by anygreat amount, the burning characteristics or magnesium and its alloys are not improved,

but instead are deleteriously aflecte'd to a very marked degree. Thus. it is necessary that the potasium content of the alloy be controlled with-j In the limits specified.

It has been further foundthat the addition of the ioregoing'amounts or potassium does not ad- I versely affect the ordinary physical properties of the aforementioned commercial magnesium al.-

- loys and in some cases there may be a slight improvement due to the addition of the potassium.

The new alloys may be compounded by any of the methods usually employed in the art for melting and alloying metals with magnesium, such as by adding the alloying ingredients either singly or jointly to a bath of molten magnesium which is preferably protected from oxidation by providing a surface blanket of a suitable flux. It is desirable that the flux should be substantially j free from magnesium chloride if the highest al- I loying emciency is-to be obtained from the po-. 3 tassium.

I claim: -1. A magnesium base alloy co'ntaining from 0.001 to 0.05 per cent of potassium, said alloy being additionally characterized by a reduced tendency to burn compared to a similar alloy not containing potassium in the aforesaid proportions;

2. In a method of reducing the tendency to burn or a magnesium base alloy in the molten state. the step which com rises incorporating in Y the alloy while molten potassium in an amount of item about 0.001 to 0.05 per oi the alloy. e

3. The method of reducing the burning characteristics in. the molten state of a'magnesium base alloy containing from 1 to 10 per cent of cent 01' the weight aluminum, from 1 to 10 per cent of zinc, and from 0.1 to 3 per cent oi! manganese, the total of the alloying metal not exceeding 20 percent and the balance being magnesium, which comprises incorporating in the alloy in the molten state ir'o 0.001 to 0.05 per cent of potassium.

4. The method of reducing the burning char-- acteristics in the molten state of a magnesium base alloy containing from 1 to 10,per cent of aluminum and from 0.1'to'3 per cent or manganese, the balance being magnesium, 'which comprises incorporating in the alloy in the molten state from 0.001 to 0.05 percent of potassium.

' 5. The method oi! reducing the burnlng'char- 1 asteristics' in the molten state of a mazl esium from 0.001 to 0.05 per cent oi potassium.

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